Spunbonded fabrics are known and they are produced from mechanically or aerodynamically drawn-off and stretched or drawn filaments or filament strands which are deposited in random texture on a conveyor belt and in this form are supplied to a bonding aggregate. In the prior art production of spunbonded fabrics with aerodynamic drawing of the filaments or filament strands and their deposition, drawing air currents are used. The energy consumption is very high because in order to avoid spinning dust deposits it is necessary to operate substantially with fresh air. Particularly in the spinning of polypropylenes and polyamides the aerosols produced at the spinning nozzle due to depolymerization of the spinning polymers tend to be precipitated in and on the drawing-off elements and to disturb the spinning as well as the web formation process. For this reason it is inadvisable to supply the air currents with recirculated air. The high energy consumption in the case of employment of fresh air must be put up with. As the air currents impinge on the perforated conveyor belt turbulence can easily be produced during the formation of the web and this turbulence adversely affects or prevents the uniformity of the filament deposition and thus of the web formation. Here, too, the spinning dust which in the spinning process is produced by the depolymerization of the polymers is troublesome inasmuch as it precipitates on the collecting screen and impairs the air permeability of the same because the filaments deposited on the web are insufficiently held down and do not come to rest in the desired optimal structure.
The high number of filaments which are spun in a large commercial plant is in most cases above 6,000 so that considerable problems arise in regard to air conduction, for the high number of filaments must be uniformly guided, conditioned, drawn and laid down. In the very large deposit area of the surfaces of 4 to 6 m width a uniform surface structure of the filament deposit must be insured. This uniform structure must be maintained, upon deposition without distortions of the web until the transfer of the still loose web to the bonding aggregate. It is known that the uniformity of the spinning webs formed of such a high number of filaments can be improved if the filaments are spun from so-called longitudinal spinning nozzles. Longitudinal spinning nozzles contain straight rows of spinning apertures and make the spinning of linear filament rovings possible. In the aerodynamic drawing of the relatively loosely guided filaments, however, the danger of entanglements arises, here too, whereby, again in the conveying-off of the freshly formed, still loosely intertwisted filaments from the range of the web formation to the zone of solidification of the web, measures must be taken to avoid air current turbulence. Such turbulence, as is well known, reduces the quality of the web structure. Also abrupt transitions of the air currents must be prevented because in this way the web becomes distorted.
In the aerodynamic drawing of filaments the elimination of spinning dust gives rise to great difficulties because the relatively loosely guided filaments, in being subjected to air blown in the drawing-off direction become easily entangled. In the case of filaments which are mechanically drawn off the spinning nozzles and drawn this danger is less pronounced since in this manner they are held under a predetermined tension between nozzle and drawing-off element so that it is possible to subject the filaments to relatively high air currents transversely of the drawing-off direction and thus to eliminate the aerosols and simultaneously cool the filaments. Mechanical drawing-off methods however are less economical compared with aerodynamic drawing methods, particularly in regard to speed of production so that in the case of modern large plants aerodynamic drawing of the filaments is preferred. In this connection it is also customary to conduct the air currents as component currents in such a manner that the drawing off of the filaments is carried out with the aid of the conditioning current and the filaments are then conducted to the perforated collecting screen serving for the deposition of the web, with a separate drawing current.